The present invention relates to a muffler shell for use in the exhaust system of a vehicle and to a muffler comprising such muffler shell according to the respective independent claim.
Mufflers are well-known components in exhaust systems of vehicles. Exhaust systems of vehicles typically comprise various components such as a manifold, one or more catalytic converters, a plurality of pipes or pipe sections, and one or more mufflers for dampening or attenuating sound. Typically, the pipes serve for the transportation of the exhaust gas, either in regions where the exhaust gas is very hot (close to the manifold or the catalytic converter) or in regions where the exhaust gas has already cooled down to some extent (in the regions of the mufflers). For a number of engines the diameter of such pipes is typically in the range of 35 mm for (smaller engines) to 70 mm (larger engines), without being limited thereto. Mufflers, on the other hand, have a much larger diameter than pipes—the cross-section of mufflers typically is at least four times larger than the cross-section of the pipes of the related exhaust system, but may be more than ten to twenty times larger than the cross-section of the pipes of the related exhaust system. A typical value for the circumference of mufflers used in a number of cars may be in the range of 400 mm to 1000 mm, without being limited thereto (their circumference may even be larger). As a consequence, the muffler shell contributes substantially to the total weight of the components of the exhaust system when compared to the pipes. Another consequence is that, due to the larger cross-section and the larger circumference of the muffler shell, the muffler shell will vibrate more easily and will therefore radiate unwanted noise, which is not a problem for the pipes having a considerably smaller cross-section and circumference. For various reasons, for example in order to reduce fuel consumption to protect the environment, there is a requirement to reduce the overall weight of the vehicle wherever possible. This requirement also relates to the various components of the exhaust system of the vehicle including the mufflers. On the other hand, mufflers must be corrosion resistant and must have a high durability so as to withstand the various mechanical stresses to which the mufflers are exposed during operation (e.g. vibrations).
Mufflers typically comprise a muffler casing comprising a muffler shell and two end pieces. The two end pieces are connected at both ends to the muffler shell either mechanically, for example by using lock seaming techniques, or by welding them to the muffler shell. In the interior of the muffler casing a number of inner parts are arranged for attenuating sound entering the muffler together with the exhaust gas, so that the level of sound exiting the muffler together with the exhaust gas is substantially lower than the level of sound entering the muffler.
Mufflers having a muffler shell comprising a single metal sheet are known. However, in order to fulfill the various requirements, in particular those mentioned above, these single metal sheet muffler shells typically are made of specific types of steel, and the sheets have a thickness of at least 0.8 mm or more.
Also known are so-called “double skin” mufflers having a muffler shell comprising two metal sheets, an inner metal sheet and an outer metal sheet. Different types of these “double skin” mufflers are known.
A first known type of “double-skin” muffler comprises an inner metal sheet and an outer metal sheet without an insulation material arranged between the inner metal sheet and the outer metal sheet. Both the inner metal sheet and the outer metal sheet are connected to the end piece (end plate), and both metal sheets are carrying the load (weight) of the inner parts of the muffler (the sound dampening parts arranged in the interior of the muffler casing). In this first type of “double-skin” muffler, both the inner metal sheet and the outer metal sheets must be able to carry the load of the inner parts of the muffler and to withstand the mechanical and vibro-acoustical stresses to which the muffler is exposed during operation of the vehicle. In addition, the inner metal sheet must be resistant to the corrosive effects of the exhaust gas while the outer metal sheet must provide for good heat insulation towards the environment, that is to say the outer sheet should not heat up to too high temperatures during operation of the vehicle. Also, the outer metal sheet must be resistant to corrosion caused by environmental substances (e.g. water splashing against the outer metal sheet during operation of the vehicle). For this first type of “double-skin” muffler, typical thicknesses are 0.4 mm to 0.6 mm for each sheet, and the total thickness for both sheets of the “double-skin” is typically in the range of 0.8 mm to 1 mm.
A second known type of “double-skin” muffler comprises an inner metal sheet and an outer metal sheet and an insulation material arranged between the inner metal sheet and the outer metal sheet. The insulation material arranged between the inner metal sheet and the outer metal sheet is intended to reduce the transmission of structure-borne sound from the inner metal sheet to the outer metal sheet so that the structure-borne sound level emitted from the muffler shell is as low as possible. A second purpose of the insulation material is to reduce the transfer of heat from the inner metal sheet, which is heated up by the hot exhaust gas flowing through the muffler, to the outer metal sheet. In this second type of “double-skin” muffler, the inner metal sheet is connected in a leak-tight manner to the end pieces (end plates) of the muffler casing first, and only then the insulation material is mounted. The outer metal sheet can then be connected to the inner metal sheet or to the end pieces (end plate) or to any component of the muffler which is sufficiently rigid to carry the load of the outer metal sheet. However, this connection of the second metal sheet does not have to be leak-tight. In this second type of “double-skin” muffler, only the inner metal sheet must be able to carry the load of the inner parts of the muffler. Also, the inner metal sheet must be able to withstand the mechanical and vibro-acoustical stresses to which the muffler is exposed during operation of the vehicle. In addition, the inner metal sheet must be resistant to the corrosive effects of the exhaust gas. The outer metal sheet must provide for good heat insulation towards the environment, that is to say the outer sheet should not heat up to too high temperatures during operation of the vehicle. Also, the outer metal sheet must be resistant to corrosion caused by environmental substances (e.g. water splashing against the outer metal sheet during operation of the vehicle). However, the outer metal sheet does not have to be able to carry the load of the inner parts of the muffler. For this second type of “double-skin” muffler, a typical thickness of the inner metal sheet is 0.6 mm or more while the outer metal sheet may have a thickness of about 0.2 mm.
Therefore, there is an ongoing need for mufflers and muffler shells having a reduced weight compared with that of prior art mufflers and muffler shells. At the same time, the mufflers and muffler shells must fulfill the afore-mentioned requirements as to corrosion resistance and as to mechanical durability.